Mixed material tubular heat exchanger

ABSTRACT

Apparatus for cooling bleed air on an aircraft may include a source of cooling fluid driven by an engine of the aircraft, a source of bleed air driven by the engine and a heat exchanger configured allow the cooling fluid to pass over tubes through which the bleed air flows. The heat exchanger may have a high-temperature zone constructed from material with a first density, and a low-temperature zone constructed from material with a second density lower than the first density.

GOVERNMENT RIGHTS

This invention was made with Government support under Contract FA8650-09-d-2922, program GE AETD Ti HX Demo awarded by U.S. Air Force. The Government has certain rights in this invention.

BACKGROUND OF THE INVENTION

The present invention relates to heat exchangers and, more particularly, to heat exchangers that may be employed in an aircraft to cool bleed air from an engine or on ground vehicles to cool exhaust gas or to heat compressed air.

In a typical turbine-engine powered aircraft, bleed air may be extracted from one or more engines and employed to operate various ancillary systems of the aircraft. For example, bleed air may be employed to drive an environmental control system (ECS), wing ice protection systems, fuel tank inerting and the like. In order to effectively use bleed air in such systems the bleed air must first be cooled after being extracted from an engine compressor.

Bleed air is usually discharged from an engine compressor at a temperature of 1200° F. or higher. The bleed air may be cooled, in one or more heat exchangers, to a temperature of about 300° F. or lower before being introduced into an ancillary system of the aircraft. Heat exchangers that are capable of withstanding inlet temperatures of 1200° F. are typically constructed from dense materials such as stainless steel or nickel based alloy.

Bleed air cooling may be performed by passing the bleed air through one or more heat exchangers which may employ ambient air as a cooling medium. In some instances, the ambient cooling air may be by-pass air propelled with a by-pass fan of the engine or ram air or air from an external fan. In this context, a heat exchanger capable of reducing temperature from 1200° F. to 300° F. must be large enough to allow for sufficient residence time of the bleed air to achieve the requisite reduction of temperature. Such a heat exchanger may be quite heavy when constructed from dense stainless steel or nickel based alloy.

As can be seen, there is a need for a system for reducing bleed air temperature without incurring a weight penalty associated with a heat exchanger constructed entirely from dense high-temperature tolerant materials.

SUMMARY OF THE INVENTION

In one aspect of the present invention, apparatus for cooling bleed air on an aircraft may comprise: a source of cooling fluid driven by an engine of the aircraft; a source of bleed air driven by the engine; a heat exchanger configured to allow the cooling fluid to pass over tubes through which the bleed air flows, the heat exchanger having, a) a high-temperature zone constructed from material with a first density, and b) a low-temperature zone constructed from material with a second density lower than the first density.

In another aspect of the present invention, a heat exchanger may comprise: a high-temperature zone constructed from material with a first density, and a low-temperature zone constructed from material with a second density lower than the first density.

In still another aspect of the present invention, a method for cooling hot fluid may comprise the steps: passing the hot fluid through first tube segments of a heat exchanger; passing the hot fluid through second tube segments of the heat exchanger directly from the first tube segments, the second tube segments having a lower temperature tolerance than the first tube segments; passing cooling fluid over the first segments to cool the hot fluid to a temperature within a range of temperature tolerance of the second tube segments; and passing the cooling fluid over the second segments to further cool the hot fluid.

These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a cooling system in accordance with an embodiment of the invention;

FIG. 2 is a perspective, partially cut-away view of a heat exchanger in accordance with a second embodiment of the invention;

FIG. 3 is exploded view of a tube of the heat exchanger of FIG. 2 in accordance with an embodiment of the invention; and

FIG. 4 is a flow chart of a method for cooling a hot fluid in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.

Various inventive features are described below that can each be used independently of one another or in combination with other features.

The present invention generally provides a system by which hot fluid such as bleed air may be cooled in a heat exchanger that has some portions of its structure comprised of low density materials.

Turning now to the description and with reference first to FIG. 1, a schematic diagram may illustrate a cooling system 100 constructed in accordance with an exemplary embodiment of the invention. An engine 102 of an aircraft (not shown) may be provided with a high-pressure bleed air port 104, an intermediate-pressure bleed air port 106 and a by-pass air port 108. A heat exchanger 110 may be positioned to receive hot fluid 111, such as bleed air, from a hot-fluid inlet line 112 and to receive cooling fluid 113, such as engine by-pass air, from a cooling-fluid inlet line 114. Cooled bleed air may be discharged through a hot-fluid outlet line 116 and by-pass air may be discharged through a cooling-fluid outlet line 118.

Referring now to FIG. 2, the heat exchanger 110 is illustrated in a simplified cut-away format. In an exemplary embodiment, the heat exchanger 110 may be constructed with multiple zones. In the embodiment of FIG. 2, three zones are illustrated: a high-temperature zone 120; a medium-temperature zone 122; and a low-temperature zone 124. Hot fluid 111 or hot bleed air may enter the heat exchanger 110 at an inlet end 126. The hot fluid 111 may pass through a plurality of tubes 128 as cooling air 113 passes over the tubes 128. Within the high-temperature zone 120 each of the tubes 128 may comprise a high-temperature segment 132. Similarly each of the tubes 128 may comprise a medium-temperature segment 134 in the medium temperature zone 122 and a low-temperature segment 136 in the low-temperature zone 124.

In an alternate exemplary embodiment, the heat exchanger 110 may comprise only two zones, the high-temperature zone 120 and the low-temperature zone 124. In such a two zone configuration, the tubes 128 may include only the high-temperature segment 132 and the low-temperature segment 136.

In an exemplary embodiment the tubes 128 may be constructed as brazed assemblies. As shown in FIG. 3, the segments 132 and 136 may be provided with at least one bell end 140. Non-bell ends 142 of the segments 134 may be inserted and brazed into the bell ends 140 of the segments 132. Similarly, the non-bell ends 142 of the segments 134 may be inserted and brazed into the bell ends 140 of the segments 136. The segments 132 may be constructed from stainless steel or a nickel-based alloy so that they are capable of withstanding high inlet temperature of 1200° F. or higher. As shown in FIG. 2, the segments 134 may be a distance D1 away from the inlet end 126 of the heat exchanger 110. The distance D1 may be great enough so that temperature of the hot fluid 111 may be reduced from about 1200° F. to about 1000° F. The segments 134 may be constructed from titanium or a titanium alloy if exposed to temperatures of 1000° F. or less. The segments 136 may be a distance D2 away from the inlet end 126 of the heat exchanger 110. The distance D2 may be great enough so that temperature of the hot fluid 111 may be reduced to about 600° F. The segments 136 may be constructed from aluminum or an aluminum alloy if exposed to temperature of 600° F. or less.

A multiple step brazing operation may be employed to construct the heat exchanger 110. In a first brazing step, the high-temperature segments 132 may be inserted into holes 151 of hot-fluid inlet manifold 150. The inlet manifold 150 may be constructed from material that can tolerate exposure to inlet temperatures of the hot fluid 111 of 1200° F. or higher. For example, the inlet manifold 150 may be constructed from the same type of material as that used for the segments 132. High-temperature brazing filler 152 may be employed to produce brazed connections between the segments 132 and the manifold 150. The brazing filler 152 must be capable of maintaining a solid connection when exposed to hot-fluid inlet temperatures of 1200° F.

In a second brazing step, the segments 134 may be brazed into a sub-assembly that includes the manifold 150 and the segments 132. As shown in FIG. 3, the ends 142 of the segments 134 may be inserted into the bell ends 140 of the segments 132. Medium-temperature brazing filler 154 may be employed to produce brazed connections between the segments 132 and the segments 134. The brazing filler 154 must be capable of maintaining a solid connection when exposed to hot-fluid temperatures of about 1000° F.

In a third brazing step, the segments 136 may be brazed into a sub-assembly that includes the manifold 150, the segments 132 and the segments 134. As shown in FIG. 3, the ends 142 of the segments 134 may be inserted into the bell ends 140 of the segments 136. Low-temperature brazing filler 156 may be employed to produce brazed connections between the segments 134 and the segments 136. The brazing filler 156 must be capable of maintaining a solid connection when exposed to hot-fluid temperatures of about 600° F.

During the third brazing step, the segments 136 may be brazed into holes 161 of a hot-fluid outlet manifold 160. The outlet manifold 160 may be constructed from the same type of material as the segments 136. The brazing filler 156 may be employed to perform brazing of the outlet manifold 160.

The heat exchanger 110 may weigh less than a high-temperature heat exchanger constructed completely from stainless steel or nickel-based alloy. The segments 134, which may be constructed from titanium or titanium alloy, may be less dense than equivalent sections of tubing constructed from stainless steel or nickel-based alloy. Similarly, the segments 136 and the outlet manifold 160 which may be constructed from materials less dense than equivalent elements constructed from stainless steel, nickel-based alloy. For example, in one of the heat exchangers with only two temperature zones, the segments 136 and the outlet manifold 160 may be titanium or titanium based alloy. In one of the heat exchangers 110 that is constructed with three temperature zones, the low-temperature segments 136 and the outlet manifold may be aluminum or aluminum based alloys. Through employment of these lower density materials the light-weight heat exchanger 110 may be particularly suited for weight-critical applications such as aircraft or other aerospace vehicles.

It may be noted that the heat exchanger 110 may be vulnerable to damage under conditions in which cooling fluid flow is interrupted while high-temperature fluid passes through the heat exchanger. Under these circumstances, the medium temperature brazing filler 154 and the low-temperature brazing filler 156 may be exposed to hot fluid temperatures of about 1200° F. However, these problematic conditions will not occur when the heat exchanger 100 is employed as an element in the cooling system 100 of FIG. 1. In the cooling system 100, the hot fluid 111, i.e., bleed air, is produced only when the engine 102 is running. The cooling fluid 113, in this case by-pass air, is continuously produced whenever the engine 102 is running. Thus cooling fluid flow will cease only when bleed air flow ceases. Consequently, the light-weight heat exchanger 110 may be employed in the cooling system 100 without concern for risk of damage that might result from cessation of cooling fluid flow.

Referring now to FIG. 4, a flow chart 400 may illustrate a method for cooling hot fluid. In a step 402, hot fluid may be passed through first tube segments of a heat exchanger (e.g., hot fluid 111 may be passed though tube segments 132 of the heat exchanger 110). In a step 404, the hot fluid may be passed through second tube segments of the heat exchanger directly from the first tube segments, the second tube segments having a lower temperature tolerance than the first tube segments (e.g. the hot fluid 111 may be passed directly from the tube segments 132 directly into the tube segments 134). In a step 406, cooling fluid may be passed over the first segments to cool the hot fluid to a temperature within a range of temperature tolerance of the second tube segments (e.g., the cooling fluid 113 may be passed over the tube segments 132). In a step 408, the cooling fluid may be passed over the second segments to further cool the hot fluid.

It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims. 

We claim:
 1. Apparatus for cooling bleed air on an aircraft comprising: a source of cooling fluid driven by an engine of the aircraft; a source of bleed air driven by the engine; a heat exchanger configured to allow the cooling fluid to pass over tubes through which the bleed air flows; the heat exchanger having, a) a high-temperature zone constructed from material with a first density, and b) a low-temperature zone constructed from material with a second density lower than the first density.
 2. The apparatus of claim 1; wherein the heat exchanger has a medium-temperature zone interposed between the high-temperature zone and the low-temperature zone; and wherein the medium-temperature zone is constructed from material with a third density lower than the first density and higher than the second density.
 3. The apparatus of claim 2 wherein the medium-temperature zone includes tube segments constructed from titanium or titanium alloy.
 4. The apparatus of claim 1 wherein the high-temperature zone includes tube segments constructed from stainless steel, nickel or nickel-based alloy.
 5. The apparatus of claim 1 wherein the low-temperature zone includes tube-segments constructed from aluminum or aluminum-based alloy.
 6. The apparatus of claim 1 wherein the source of cooling fluid is a by-pass fan of the engine.
 7. The apparatus of claim 1: wherein the heat exchanger includes a hot-fluid inlet manifold constructed from the material with the first density; and wherein the heat exchanger includes a hot-fluid outlet manifold constructed from the material with the second density.
 8. A heat exchanger comprising: a high-temperature zone constructed from material with a first density, and a low-temperature zone constructed from material with a second density lower than the first density.
 9. The heat exchanger of claim 8 further comprising a medium-temperature zone interposed between the high-temperature zone and the low-temperature zone, wherein the medium-temperature zone is constructed from material with a third density lower than the first density and higher than the second density.
 10. The heat exchanger of claim 9 wherein the medium-temperature zone includes tube segments constructed from titanium or titanium-based alloy.
 11. The heat exchanger of claim 9 comprising: a plurality of hot-fluid passage tubes, each of the tubes including, a) a high-temperature tube segment constructed from the material with the first density, b) a low-temperature tube segment constructed from the material with the second density and c) a medium-temperature tube segment constructed from material with a third density, said third being lower than the first density and higher than the second density.
 12. The heat exchanger of claim 8 wherein the high-temperature zone includes tube segments constructed from stainless steel, nickel or nickel-based alloy.
 13. The heat exchanger of claim 8 wherein the high-temperature zone includes tube segments constructed from titanium or titanium-based alloy.
 14. The heat exchanger of claim 8 wherein the low-temperature zone includes tube-segments constructed from aluminum, aluminum-based alloy, titanium or titanium alloy.
 15. The heat exchanger of claim 8 further comprising: a hot-fluid inlet manifold constructed from the material with the first density; and a hot-fluid outlet manifold constructed from the material with the second density.
 16. The heat exchanger of claim 15: wherein the medium-temperature tube segments are brazed to the high-temperature tube segment with a first brazing filler that remains solid at a temperature of at least 1000° F.; and wherein the medium-temperature tube segments are brazed to the low-temperature tube segments with a second brazing filler that remains solid at a temperature of at least 600° F.
 17. The heat exchanger of claim 15 wherein the high-temperature tube segments are brazed to a hot-fluid inlet manifold with brazing filler that remains solid at a temperature of at least 1200° F.
 18. A method for cooling hot fluid comprising the steps: passing the hot fluid through first tube segments of a heat exchanger; passing the hot fluid through second tube segments of the heat exchanger directly from the first tube segments, the second tube segments having a lower temperature tolerance than the first tube segments; passing cooling fluid over the first segments to cool the hot fluid to a temperature within a range of temperature tolerance of the second tube segments; and passing the cooling fluid over the second segments to further cool the hot fluid.
 19. The method of claim 18 further comprising the steps: passing the hot fluid through third tube segments of the heat exchanger, the third tube segments having a lower temperature tolerance than the second tube segments; passing the cooling fluid over the second segments to cool the hot fluid to a temperature within a range of temperature tolerance of the third tube segments; and passing the cooling fluid over the third segments to further cool the hot fluid.
 20. The method of claim 18: wherein the hot fluid is bleed air driven with an engine of the aircraft; and wherein the cooling fluid is by-pass air driven by the engine. 